Financial rules of thumb are just that. If you follow them, you have the satisfaction of knowing that you’ve taken action — but they do not guarantee you’ll get the results you desire. Still, in the savings game guideposts can be especially useful. A near-term target will help you get started, and that’s half the battle.

Fidelity Investments recently put together an age-based savings guideline with a range of savings goals. It’s meant to prod individuals into action, which it might—if, that is, the firm’s daunting assumptions don’t discourage them first.

At age 35, you should have saved an amount equal to your annual salary.

At age 45, you should have saved three times your annual salary.

At 55, you should have five times your salary.

When you retire at age 67, you should have eight times your annual pay.

Others have tried to divine a finishing multiple of salary that ensures retirement happiness, and generally they are in line with Fidelity’s target. Consultants Aon Hewitt set the goal at 11 times final pay (by age 65).

What Fidelity ads to the discussion are benchmarks to hit along the way. Having near-term targets helps you stay on track—and to take steps to catch up while time is on your side. But there is nothing easy about hitting these targets. Fidelity assumes:

You begin saving in a workplace retirement plan, such as a 401(k), at age 25. You save continuously and without interruption until age 67.

You start by making an annual salary contribution equal to 6% of pay, and raise the figure by one percentage point each year until you are saving 12% of pay.

Your employer matches you at 50 cents on the dollar up to 6% of pay and your portfolio grows 5.5% a year.

These assumptions are reasonable in terms of building an illustrative savings model. But consider that almost no one starts saving at 25 and millions suffer some sort of job interruption over a 42-year career. This model also has you saving 12% of pay by age 32. A common rule of thumb is 10% and, again, most folks don’t get serious about saving until they are in their 40s and 50s.

Meanwhile, you will need a healthy slug of stocks to earn 5.5% a year. Yet individuals have been net sellers of stock mutual funds for at least half a decade. Whether Social Security will be available when you retire is an open question. And many peoples’ wages are going down—not up by more than the rate of inflation.

Of course, it would be a mistake to extrapolate the experience of the crisis years indefinitely into the future. Still, this exercise points up the difficulty of reaching retirement security without an early start, or hyper-aggressive saving at midlife. No matter your age, at least now you can see where you stand–and what to do about it.

Dan Kadlec is a journalist who has written about personal finance for TIME and other outlets for 25 years. He is the author of three books, a leading voice in the global financial literacy movement, and strategic adviser to the National Financial Educators Council.

Kadlec's latest is A New Purpose: Redefining Money, Family, Work,Retirement, and Success